PhET
Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations...
Physics, Biology Chemistry, Earth Science, Maths
Maths, English Language Arts, Science, Social Studies, Art, Music, etc.
Interactive Sites for Education
All of the best K-5 online, interactive, educational games and simulations in one place...